Experimental Evaluation of the Nukiyama-Tanasawa Equation for Pneumatically Generated Aerosols Used in Flame Atomic Spectrometry

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Abstract
The Nukiyama-Tanasawa equation has been checked for its applicability to predict the Sauter mean diameter of aerosols generated pneumatically under the conditions usually employed in FAAS. The measurements of droplet-size distribution have been carried out by means of a laser Fraunhofer diffraction system. The effects of both gas and liquid flows, and solvent physical properties, on experimental and calculated Sauter mean diameters of the aerosols have been studied. The results show that this equation, under normal conditions used in FAAS, correctly describes the trends of Sauter mean diameter variation of aerosols generated pneumatically with respect to the flows of nebulizing gas and liquid. Increases in liquid flow or decreases in gas flow give rise to increases in Sauter mean diameters of the aerosols. However, the absolute values predicted according to the equation far exceed the experimental Sauter mean diameters obtained, the divergences being larger at higher liquid flow/nebulizing gas flow ratios. The overestimation for water ranged from 1.8- to 8.1-fold, and for organic solvents and methanol+water mixtures from 3.6- to 13.3-fold. Under the conditions studied, experimental Sauter mean diameter values for the organic solvents and methanol+water mixtures studied were well below those found for water, under comparable conditions. This result contradicts the predictions of the Nukiyama-Tanasawa equation mainly at high liquid flow/nebulizing gas flow ratios. The main reason for this divergence is the overweighting assigned to the second term of the equation.